1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method thereof, and more particularly to a liquid crystal display device to which an improvement of an alignment film is applied and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display device is a display device which adjusts a quantity of transmitting light from a light source by controlling the direction of liquid crystal molecules with an electric field.
In a TN (Twisted Nematic) mode, an IPS (In-Plane Switching) mode, and a VA (Vertical Alignment) mode which are applied to many active matrix display devices currently, it is necessary to create a stable alignment state and hence, it is necessary to form an alignment film on at least one of opposedly-facing surfaces of a pair of substrates which sandwich a liquid crystal layer therebetween.
Particularly, in the TN mode and the IPS mode, in principle, it is necessary to perform treatment which imparts an ability of controlling the alignment in the fixed direction to at least one of opposedly-facing surfaces of the pair of substrates. Further, in the VA mode, it may be possible to control initial driving of the liquid crystal molecules by forming projections or stripes on at least one of opposedly-facing surfaces of the pair of substrates. However, in forming these projections or stripes, there exists a possibility that the throughput is lowered at the time of forming the projections or the stripes. On the other hand, when neither projections nor stripes are formed, it is necessary to impart an ability of controlling the alignment in the particular direction with respect to an alignment film.
There may be a case where surface unevenness is provided to a background of the alignment film. For example, the liquid crystal display device adopts the constitution in which spacers (hereinafter referred to as pillar-shaped spacers) are arranged on one of opposedly-facing surfaces of the pair of substrates in place of scattering bead spacers as separate members, and spacer pedestals which are arranged to face the pillar-shaped spacers in an opposed manner are formed on another opposedly-facing surface.
To consider a case where an impact is applied to the liquid crystal display device having such a constitution, when the spacer and the spacer pedestal are brought into contact with each other, an alignment film on a surface of the spacer is abraded or peeled off thus giving rise to drawback that bright spots are generated thus causing a display defect.
A technique which can overcome this drawback is disclosed in JP-A-2000-267114 (patent document 1).
Patent document 1 states that the above-mentioned drawback can be overcome by making a film thickness of an alignment film on a top surface of a spacer smaller than a film thickness of the alignment film on portions other than the top surface of the spacer (or setting the film thickness of the alignment film on the top surface of the spacer to zero). In other words, the drawback can be overcome by applying an alignment film material and, thereafter, by performing time-prolonged leveling corresponding to viscosity by prolonging a time for leveling. To be more specific, patent document 1 states “a solution containing polyimide is applied by coating to the whole surface of a glass substrate on which pixel electrodes are formed by offset printing, a coated film is leveled for 60 seconds, and the leveled coated film is dried at a temperature of 100° C., and is baked at a temperature of 180° C. for 1 hour thus forming an alignment film having a thickness of 1000 angstrom. Thereafter, rubbing treatment is applied to the alignment film.” That is, due to (A): “leveling processing”, an organic solvent containing the alignment film material arranged on an upper surface of a projection is moved to a low place around the projection and hence, the organic solvent is leveled. By prolonging this time, “local reduction of film thickness” of the alignment film on the projection can be realized. Further, due to (B): “baking process”, the organic solvent is evaporated so that “the reduction of film thickness at a fixed ratio over the whole surface” of the alignment film can be realized. With respect to the alignment film to which rubbing treatment is applied, the film thickness of the whole alignment film is substantially determined through these two reduction-of-film-thickness processes.